Multiple sheath cable and method of manufacture

ABSTRACT

A multiple sheath cable for telemetry, heating and communications and methods of manufacturing such cable in long lengths with high tensile strength. The telemetry and communications cable may be of the wire type for conducting electrical signals or fiber optics for conducting laser or other optical signal, the conductors being typically insulated by mineral insulation material or organic insulation material. These insulated conductors are provided with concentric multiple layers of metal tubular sheaths having staggered weld joints for increasing tensile strength while protecting the conductors and the insulation from extreme environmental conditions such as heat, pressure and corrosion.

This is a division of application Ser. No. 112,933, filed Jan. 17, 1980,now U.S. Pat. No. 4,317,003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrical and fiber optic cables andmethods of manufacturing such cables in long single lengths by providinga multiple sheath with staggered weld joints for increased strength andenvironmental protection.

2. History of the Prior Art

In the drilling and maintenance of deep oil wells and geothermic wells,it is necessary to periodically lower temperature and pressure probes,gauges and other telemetry equipment into the well to take bottom holemeasurements.

Since some of these wells are at depths ranging from 15,000 to 40,000feet, the tensile strength of the telemetry cable must be extremely highto support the weight of the equipment in addition to the weight of thecable due to the length thereof. Further, the cable may be exposed toextreme temperatures, pressures and highly corrosive materials whileinside the well.

The cables that could be used for such deep well logging are of thestainless steel jacketed mineral oxide type cables typically used asheater cables as taught in U.S. Pat. No. 4,137,762, issued Feb. 6, 1979to William D. Smith.

However, present methods of manufacture of such cable result in cablesof limited length. These limitations in length are primarily due to thelimited lengths of available strip stock material being used. Further,in order to jacket cable with material such as stainless steel, thestrip stock must be rather thin so that it can be bent around the wireand the insulation. This use of relatively thin material will not yieldthe necessary tensile strength for such deep hole telemetry operations.

Further, if ordinary splicing techniques are used, the tensile strengthat the splice joint is less than that of the cable itself and hence cangive rise to localized failures.

Also, in the manufacture of such cables shorter lengths naturally occurdue to random weld failures along the sheath seam which leaves holes inthe seam requiring the cable to be cut at that point. This cutting atrelatively short lengths is quite acceptable in the heater cable usagesince often there is a use for short cables but would be totallyunacceptable in producing telemetry cable for deep hole weld loggingoperations.

Recently, a second need for long cable lengths with high tensilestrength has developed in the form of fiber optic communications cable.Telephone companies are now experimenting with fiber optic lengths inexcess of one mile and which are to be buried in trenches therebysubjecting the cable to harsh environments.

Such cables must have considerable tensile strength due to the handlingof the long lengths thereof and while high temperatures are not normallypresent in such usage, other environmental conditions exist such ascorrosive earth environments and heavy lateral loads which might tend tocrush the cable.

Since it is very difficult to splice fiber optic bundles and since suchmaterial exhibits a relatively low tensile strength, it would benecessary to jacket the cables with a protective sheath having highresistance to corrosive surroundings, high tensile strength andresistance to crushing lateral loads.

Still another use for metal jacketed cable is for the protection ofpower cables in extreme environments where reliability is essential.

SUMMARY OF THE INVENTION

The present invention provides a multiple sheath cable and a method ofmanufacturing the cable in extremely long continuous lengths with hightensile strength and to provide the protection necessary to overcome theproblems hereinbefore set forth.

The present invention provides a method of splicing metal-jacketedmineral insulated cable and a design and method for reinforcing thesheath joints by multiple sheath layering techniques.

Another object of the invention is to provide a multiple layered sheathfor protecting fiber optic cable and organic insulated wires.

In the case of mineral insulated cables, cable segments manufactured ina conventional manner are spliced together using a design and methodwhich does not create an appreciable increase in diameter of the splicejoint. This is basically accomplished by trimming back a portion of thesteel jacket from the abutting ends of two cable segments and thenremoving the insulation from that open portion to expose the conductoror conductors therein.

The conductors and the abutting end portions of the steel jacket arethen joined by welding or soldering techniques thereby leaving a windowarea open at the splice joint. Mineral insulation of a flowableconsistency is poured into the open area to cover the conductor wires ormay be inserted in the form of shaped molded insulation blocks.

The open window then is covered by a shaped segment of stainless steeltube material and welded into place thereby forming a splice joint ofsubstantially the same diameter as the cable segments.

After the total desired cable length has been made up and wound onto adrum, the cable may be drawn or roll reduced to pack the insulation inand about the splice joints. The cable then may be cleaned and treatedwith a sealant or bonding agent.

This finished cable length is then run through a sheathing machine ortube mill which will form another sheath over the original sheath. Thisis typically done by seam welding. During the application of the secondsheath it may be necessary to splice the metal strip prior to beingwrapped around the original, care being taken so that each splice jointis a good distance from any splice join in the original sheath. It isfelt that a minimum of ten meters between splice joints of successivewraps for most small cables would be sufficient.

After the second layer of sheathing has been added, the cable may bedrawn or roll reduced very tightly onto the original sheath. Also duringthe application of this second sheath, weld flaws might occur. The weldquality is monitored and weld flaws should be patched prior to thedrawing or roll reduction of the second sheath.

More subsequent layers of sheathing material may be added in the samemanner as hereinbefore set forth. When drawing or roll reducing thecable in carrying out the steps hereinbefore set forth, it may benecessary to anneal the sheath to prevent too much work hardening whichcould cause breaking or cracking. The finished cable may then be drawnor roll reduced to increase tensile strength or to meet production sizerequirements.

In the sheathing of cables having optical fibers or plastic insulatedconductors, the weld patching of the sheath or annealing might damagethe materials inside the cable and hence those steps would have to beeliminated.

The manner of multiple sheathing such cables would be either tomanufacture a continuous length of such cable in the desired length orsplice together cables which are adaptable for such splicing such asplastic insulated conductor cable prior to the adding of the first metalsheath which typically would be stainless steel.

After the desired length of cable has been made up, the cable could becleaned and coated with a sealing material such as an anaerobic adhesiveor heat sensitive or pressure sensitive adhesive. The cable is then runthrough a sheathing machine or tube mill which will form a steel jacketwith a seam weld. Experimentation has shown that the speed of welding insuch a sheathing machine or tube mill is sufficient to prevent localizedheat which would damage the insulation material in the original cable.

This original sheath may then be roll reduced or drawn in order toprovide a tight-fitting steel jacket around the insulated cable.

The outside surface of this cable may then be cleaned and provided witha suitable sealant or bonding coating to prepare for the application ofthe second sheath. If weld flaws occur during the application of thesecond sheath, the weld quality should be monitored and unwelded jointsor holes should be patched with a semiflexible sealant such as siliconrubber or solder which can be applied without damage to the cable or theinsulation in the cable. This patching is done just prior to the drawingor roll reduction.

More subsequent layers of sheathing material may be added in the samemanner as hereinbefore described, always staggering the weld joints toinsure that no two weld joints occur at the same longitudinal location.

Since the tensile strength to weight ratio of stainless steel is ratherhigh, for most practical applications several layers of stainless steelmay be added in order to provide a tensile strength high enough to beable to safely lower equipment into deep well bores with the assurancethat the equipment will not be lost due to cable breakage and with thefurther assurance that there will be sufficient resistance totemperature, pressure and corrosion to protect the conductor wires.

On the other hand, in protecting fiber optics or plastic coatedconductors which would normally not be used in deep well operations dueto temperature restrictions, the added tensile strength is not so muchto support the weight of long lengths of cable but to be able to handlesuch long lengths of cable during trenching operations with addedassurance of not encountering breakage which gives rise to an unwantedsplice joint.

Further, in the use of fiber optics or conductor cable which is used forpower or communications, where high reliability is essential, themultiple stainless steel sheathing serves to protect the cable againstcorrosive environments after it has been laid.

DESCRIPTION OF THE DRAWINGS

Other and further advantageous features of the present invention willhereinafter more fully appear in connection with a detailed descriptionof the drawings in which:

FIG. 1 is a side sectional view of a multiple sheath cable embodying thepresent invention.

FIG. 2 is an end sectional view of the cable of FIG. 1 taken along thebroken lines 2--2 of FIG. 1.

FIG. 3 is an elevational schematic view of a machine for applyingmultiple sheathing under the teachings of the present invention.

FIGS. 4, 5 and 6 are perspective views of a mineral insulated cablesection depicting the method of splicing said cable.

FIG. 7 is a side sectional view of the finished splice joint of thecable of FIGS. 4, 5 and 6.

FIGS. 8, 9 and 10 are perspective views of cable segments showing asplice joint where two conductors are present in the cable.

FIGS. 11, 12 and 13 show perspective views of a three-conductor cablesplice joint.

FIG. 14 depicts an end sectional view of a fiber optic bundle having amultiple metal sheath embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings in detail, reference character 10 generallyindicates a multiple sheath cable which in this case depicts a singleconductor 12 surrounded by mineral insulation such as magnesium oxide14, which in turn is surrounded by a stainless steel first sheath member16. FIG. 1 of the drawings, at reference character 18, depicts a splicejoint in the mineral insulated cable which will be hereinafter morefully described.

Second, third and fourth tubular metal sheaths 20, 22 and 24 are alsoshown in FIG. 1, each depicting at least one butt-welded splice joint26, 28 and 30, respectively. As will be hereinafter set forth, it isdesirable in the practice of the present invention that the butt-weldedsplice joints 26, 28 and 30 be longitudinally spaced with respect to thecable so that none of the splice joints are superimposed over anotheradjacent splice joint. It is further noted that each of the sheathmembers 16, 20, 22 and 24 are all seam-welded at 32, 34, 36 and 38,respectively.

It is further desirable that the seam-weld lines also be staggered sothat one seam-weld does not fall directly over another adjacentseam-weld as shown in FIG. 2. Further staggering of these seam-weldedjoints may be accomplished by the way in which the cable is rolled andhandled between successive applications of sheaths.

Referring now to FIG. 3 of the drawings, reference character 40generally indicates a sheathing machine or tube mill which may be usedfor not only applying the first layer 16 of sheathing but may also beused and is shown here as being used to apply a subsequent layer ofsheathing to already prepared cable.

The machine 40 generally comprises a spool 42 for carrying strip stockstainless steel 44 thereon. The strip 44 is payed off the spool 42 andmay be spliced in the area indicated at 46 in order to obtain thedesired lengths. This splicing is typically accomplished by a butt-weldand which shows up in the finished cable as the butt-welds 26, 28 and30.

The stock 44 is then fed through a plurality of forming rollers 48, 50,52 and 54 wherein the edges of the material are rolled up to form atrough so that the strip stock exits the forming rolls 54 with asubstantially U-shaped cross-section at 56 for receiving a strip ofcable material 58 therein.

The cable material 58 is payed off of a spool 60 which is located abovethe tube mill and may be substantially any size depending on the amountof cable to be carried thereby. This cable may be in the form of steeljacketed mineral oxide cable as shown in FIG. 1 or may be any form ofcable covered by a mineral insulation or an organic insulation such asplastic.

After the cable 58 enters the trough-shaped sheath material 56, thecombination enters closing rollers 62 which closes the stainless steelsheath into a tubular configuration and while being held in a closedposition, the seam is continuously welded by the welding device 64 whichmay be a tungsten inert gas welder or other suitable welding machine. Ithas been found that the combined cable and sheath may move through thetube mill 40 fast enough that the seam-welding accomplished by thewelding device 64 does not appreciably raise the temperature of thesheath to damage the cable being closed therein. Hence, if the innercable 58 happens to have an organic insulation such as plastic or in thecase of fiber optic material, insulated by plastic, no damage is donewithin the cable. However, if the cable 58 is of the mineral oxide steeljacketed type, the heat would be of little significance.

After the seam has been welded, it should be monitored to detect anyweld flaws so that such weld flaws may be patched in the area generallyindicated by reference character 66.

In the case of mineral insulated cable the patch can be accomplished bywelding techniques whereas if the interior cable 58 is of a plasticinsulation or insulation subject to damage by heat, the patching shouldbe done by way of a semiflexible sealant such as silicone rubber orsolder which can be applied without damage to the interior cable.

After necessary repairs are made where weld flaws occur, the cablepasses through a tube reducing device 68 which can be in the form of adraw dye or reducing rollers to compress the outer sheath material 44 infirm engagement with the cable 58 carried therein. After the cable hasbeen roll reduced or drawn to be reduced in the device 68, it may bedesirable to provide an annealing operation at 70 or by the use of aseparate facility in order to prevent damage due to work hardening.However, annealing would not be permissable where the insulation isplastic. In either case, the cable may then be rolled onto a suitablespool 72.

It can readily be seen that the spool 72 might have its axis 74 locatedat substantially any angle with respect to the vertical plane containingthe tube mill in order to stagger the seam weld joints 32, 34, 36 and 38in any desired manner. Opposing weld joints as shown in FIG. 2 may beaccomplished by simply inverting the spools between successiveapplications of sheathing material.

Typically one would probably either have adjustable rollers in a singletube mill machine or have three or four tube mill machines havingdifferent sized rollers for the application of the subsequent layers ofstainless steel sheathing on the cable.

Referring now to FIGS. 4 through 7, reference characters 76 and 78represent end segments of a mineral insulated single wire conductorwhich are to be spliced together to form an initial desired length ofcable. Both of the cables 76 and 78, for the purpose of this example,contain a central conductor wire 76A surrounded by mineral insulation76B which in turn is surrounded by a steel jacket or sheath 76C.Likewise, the cable 78 has a central conductor 78A surrounded by mineralinsulation 78B and again which is surrounded by a stainless steel sheath78C. A portion of the sheaths 76C and 78C are cut away and the mineralinsulation contained therearound is removed thereby leaving exposed aportion of the sheaths 76C and 78C and the conductor wires 76A and 78Aas shown in FIG. 4.

The ends of the sheath are then butted together as shown in FIG. 5 andprovided with a butt-weld indicated by reference character 80 andwherein the ends of the conductors 76A and 78A are joined by eitherwelding or soldering at reference character 82. This leaves a windowarea generally indicated by reference character 84 which exposes theinside of the adjoining sheath and the conductor. A half cylinder moldedblock 86 of insulation material may then be inserted into the windowarea 84 as shown in FIGS. 5 and 6 and rotated into the bottom portionthereof as shown in FIG. 6.

A second similar molded block 88 of insulation material may then belowered into place to finish filling the window area 84 as shown in FIG.6 and covered by a section of stainless steel tube stock 90. This pieceof tube stock 90 then is welded in place to close the window area 84 andto form a splice joint which will not appreciably change the diameter ofthe cable. FIG. 7 then shows a sectional view of the splice joint wichis similar to the section 18 as shown in FIG. 1. But which also depictsthe weld joint 92 at the place member 90. FIGS. 8, 9 and 10 depict amethod of splicing segments 94 and 96 of a two-conductor cable wherein afirst molded piece of insulation 98 is inserted into position within thewindow area before the segments 94 and 96 are butted together forwelding. A possible problem that could be associated with this processwould be the requirement of welding or soldering the conductor endstogether when they are in contact with the molded insulation piece 98. Asecond molded insulation block 100 then is inserted into place tocompletely fill the window area and is covered by a piece of tubularstock 102 which is cut to fit over the window area for subsequentwelding into place as shown in FIG. 10 by reference character 104.

Referring to FIGS. 11, 12 and 13, three conductor cables 106 and 108 maybe joined by forming the window as herinbefore set forth and butting thecable ends together, butt-welding the sheath at 110 and soldering orwelding the wire segments together. Insulation material then of aflowable nature such as granular insulation or insulation in a solution,may then be poured into the open window area and thereby the window areais filled with such insulation at 112 as shown in FIG. 13. Molded blocks114 and 116 may then be inserted to finish filling the window area. Thewindow area may be thereafter capped with a suitable piece of stockmaterial 118 and welded in place.

It should be pointed out that after the splice has been accomplished bythe methods hereinbefore set forth, it may be necessary to pass thecable through a roll reducing or draw dye in order to compact theinsulation around the splice joints and throughout the cable.

Referring now to FIG. 14, reference character 120 generally indicates afiber optic cable having multiple metal sheaths. Often the fiber opticscable is provided in an array 122 which is then covered by a pluralityof plastic insulation sheaths generally indicated by reference character124. In this particular case, the outer surface of the cable is coveredby a reinforced plastic sheath 126.

In order to further reinforce this cable, it is passed through a tubemill or sheathing machine whereby a layer of stainless steel sheathing128 is applied in the manner as hereinbefore set forth and possibly by amachine such as the tube mill 40 of FIG. 3.

Additional layers of sheathing 130 and 132 may also be applied ashereinbefore set forth, taking care to stagger the weld joints and tonot expose the cable to localized temperatures which would cause meltingof the plastic sheathing.

As hereinbefore set forth, seam welding may be accomplished by acontinuous tube mill 40 without damage to the insulation material.However, where localized heating may occur during patching or repairingby welding techniques, suitable cool patching techniques should beaccomplished as hereinbefore set forth.

From the foregoing, it is apparent that the present invention provides amultiple sheath cable having greatly enhanced tensile strength forprotection of the conductors whether they be electrical conductors orfiber optic conductors, against corrosion and pressure. The foregoingalso provides splicing techniques which are effective in the splicing ofmineral insulated cable in preparation for applying the multiplestainless steel sheaths for increased strength and protection.

Whereas the present invention has been described in particular relationto the drawings attached hereto, other modifications apart from thoseshown or suggested herein may be made within the spirit and scope of theinvention.

What is claimed is:
 1. A method of manufacturing multiple sheath cable in long lengths comprising the steps of:(a) applying a first continuous metal sheath to an insulated conductor of the desired length; (b) splicing the first continuous metal sheath at locations radially and longitudinally spaced from any conductor splice joints; (c) reducing the diameter of the first metal sheath to tightly grip the insulated conductor; and (d) applying second and subsequent metal sheaths to the first sheath repeating steps (a), (b) and (c).
 2. A method of manufacture as set forth in claim 1 and including the step of thoroughly cleaning the next preceding sheath before applying a subsequent sheath.
 3. A method of manufacture as set forth in claim 1 and including the step of patching flaws in the application of each sheath just prior to the step of reducing the diameter thereof.
 4. A method of manufacture as set forth in claim 1 and including the step of cleaning and coating the surface of the next preceding sheath with a sealing and bonding agent before applying a subsequent sheath.
 5. A method of manufacture as set forth in claim 1 and including the step of annealing the cable between applications of metal sheaths to prevent damage due to work hardening.
 6. A method of manufacturing multiple sheath mineral insulated cable in long lengths comprising the steps of:(a) splicing together in end-to-end relationship, a plurality of metal jacketed mineral insulated cable segments containing at least one conductor; (b) applying a first continuous metal sheath to said mineral insulated cable; (c) splicing the metal sheath at locations radially and longitudinally spaced from any splice joints of the mineral insulated cable; (d) reducing the diameter of the first metal sheath to tightly grip the mineral insulated cable; (e) applying second and subsequent metal sheaths to the first sheath by repeating steps (b), (c) and (d).
 7. A method of manufacture as set forth in claim 6 wherein the step of splicing together the mineral insulated cable comprises the steps of cutting back a portion of one side of the metal jacket of each abutting end piece; removing the insulation in the cut-back portion exposing the at least one conductor; butt-welding the conductors of the two end pieces; butt-welding abutting ends of the remaining portion of the metal jacket to leave a window area; filling the window area with mineral insulation around the conductor; and welding a metal jacket portion over the window area, all without appreciably increasing or changing the overall diameter of the metal jacketed cable.
 8. A method of manufacture as set forth in claim 7 wherein the filling of the window area is done by pouring flowable mineral insulation material into said window area around the conductor or conductors.
 9. A method of manufacture as set forth in claim 7 wherein the step of filling the window area is accomplished by inserting a plurality of shaped, molded insulation blocks into the window area around the conductor. 